Field of the Invention
This invention generally relates to optical correction, and in exemplary embodiments provides methods, devices, and systems for mitigating or treating defects of the eye. Among the exemplary embodiments, the invention may provide multifocal intraocular lenses.
Background
Presbyopia is a condition that affects the accommodation properties of the eye. As objects move closer to a young, properly functioning eye, the effects of ciliary muscle contraction and zonular relaxation allow the lens of the eye to become rounder or more convex, and thus increase the optical power and ability of the eye to focus at near distances. Accommodation can allow the eye to focus and refocus between near and far objects.
Presbyopia typically develops as a person ages, and is associated with a natural progressive loss of accommodation. A presbyopic eye often loses the ability to rapidly and easily refocus on objects at varying distances. The ability to focus on objects at near distances may also diminish with the presbyopic eye. Although this condition progresses over the lifetime of an individual, the effects of presbyopia usually become noticeable after the age of 45 years. By the age of 65 years, the crystalline lens has often lost almost all elastic properties and has only a limited ability to change shape, or residual accommodation. Residual accommodation refers to the amount of accommodation that remains in the eye. A lower degree of residual accommodation contributes to more severe presbyopia, whereas a higher amount of residual accommodation correlates with less severe presbyopia.
Along with reductions in accommodation of the eye, age may also induce clouding of the lens due to the formation of cataracts. Cataracts may form in the hard central nucleus of the lens, in the softer peripheral cortical portion of the lens, or at the back of the lens. Cataracts can be treated by the replacement of the cloudy natural lens with an artificial lens. Phacoemulsification systems often use ultrasound energy to fragment the natural lens and aspirate the lens material from the eye. An artificial lens replaces the natural lens in the eye, with the artificial lens often being referred to as an intraocular lens (IOL).
After replacement of the natural lens with an intraocular lens, patients may have little or no ability to adjust the optical power associated with the optical tissues of the eye so as to maintain visual quality when changing viewing distance (for example, between viewing a far object while driving and viewing a near object while reading small print). Fortunately, a variety of technologies have been developed that enhance the ability of IOLs to facilitate viewing objects at different distances. Multifocal IOLs may, for example, rely on a diffractive optical surface to direct portions of the light energy toward differing focal distances, thereby allowing the patient to see both near and far objects.
While generally successful at mitigating presbyopia, as with all successes, still more improvements would be desirable. With existing multifocal IOLs, the performance and patient satisfaction may depend on several aspects related to the individual patient. As a result, not all patients are satisfied with multifocal IOLs after implantation for a variety of reasons.
In light of the above, it would be desirable to provide improved IOLs for cataract patients and others. IOL lens design may include a compromise among various design objectives. It would be particularly beneficial if these improved IOLs could take advantage of the capabilities of diffractive multifocal optics, and would enhance patient satisfaction by having optical attributes that are more tailored to the needs and desires of the patient.